Attempting to explain heterogeneous HIV epidemics in sub-Saharan Africa: potential role of historical changes in risk behaviour and male circumcision

HIV trends and disparities by gender and urban-rural residence among adolescents in sub-Saharan Africa

Background

In sub-Saharan Africa HIV transmission is a major challenge in adolescents, especially among girls and those living in urban settings. Major international efforts have aimed at reducing sexual transmission of HIV. This analysis aims to assess the trends in HIV prevalence by gender in adolescents, as well as urban–rural disparities.

Methods

HIV prevalence data at ages 15–19 years were obtained for 31 countries with a national survey since 2010 and for 23 countries with one survey circa 2005 and a recent survey circa 2015. Country medians and average annual rates of changes were used to summarize the trends for two subregions in sub-Saharan Africa, Eastern and Southern Africa and West and Central Africa, which largely correspond with higher and lower HIV prevalence countries. Data on HIV incidence at ages 15–24 and prevalence at 5–9 and 10–14 years were reviewed from 11 recent national surveys. Trends in urban–rural disparities in HIV prevalence and selected indicators of sexual and HIV testing behaviours were assessed for females and males 15–24 years, using the same surveys.

Results

HIV prevalence among girls 15–19 years declined in eastern and Southern Africa from 5.7 to 2.6% during 2005–2015 (country median), corresponding with an average annual rate of reduction of 6.5% per year. Among boys, the median HIV prevalence declined from 2.1 to 1.2%. Changes were also observed in West and Central Africa where median HIV prevalence among girls decreased from 0.7 to 0.4% (average annual rate of reduction 5.9%), but not for boys (0.3%). Girl-boy differences at 10–14 years were small with a country median HIV of 1.0% and 1.3%, respectively. Urban females and males 15–24 had at least 1.5 times higher HIV prevalence than their rural counterparts in both subregions, and since the urban–rural declines were similar, the gaps persisted during 2005–2015.

Conclusions

HIV prevalence among adolescents declined in almost all countries during the last decade, in both urban and rural settings. The urban–rural gap persisted and HIV transmission to girls, but not boys, is still a major challenge in Eastern and Southern African countries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12978-021-01118-7.

Couple serostatus patterns in sub-Saharan Africa illuminate the relative roles of transmission rates and sexual network characteristics in HIV epidemiology

HIV prevalence has surpassed 30% in some African countries while peaking at less than 1% in others. The extent to which this variation is driven by biological factors influencing the HIV transmission rate or by variation in sexual network characteristics remains widely debated. Here, we leverage couple serostatus patterns to address this question. HIV prevalence is strongly correlated with couple serostatus patterns across the continent; in particular, high prevalence countries tend to have a lower ratio of serodiscordancy to concordant positivity. To investigate the drivers of this continental pattern, we fit an HIV transmission model to Demographic and Health Survey data from 45,041 cohabiting couples in 25 countries. In doing so, we estimated country-specific HIV transmission rates and sexual network characteristics reflective of pre-couple and extra-couple sexual contact patterns. We found that variation in the transmission rate could parsimoniously explain between-country variation in both couple serostatus patterns and prevalence. In contrast, between-country variation in pre-couple or extra-couple sexual contact rates could not explain the observed patterns. Sensitivity analyses suggest that future work should examine the robustness of this result to between-country variation in how heterogeneous infection risk is within a country, or to assortativity, i.e. the extent to which individuals at higher risk are likely to partner with each other.

Measuring and modelling concurrency

This article explores three critical topics discussed in the recent debate over concurrency (overlapping sexual partnerships): measurement of the prevalence of concurrency, mathematical modelling of concurrency and HIV epidemic dynamics, and measuring the correlation between HIV and concurrency. The focus of the article is the concurrency hypothesis - the proposition that presumed high prevalence of concurrency explains sub-Saharan Africa's exceptionally high HIV prevalence. Recent surveys using improved questionnaire design show reported concurrency ranging from 0.8% to 7.6% in the region. Even after adjusting for plausible levels of reporting errors, appropriately parameterized sexual network models of HIV epidemics do not generate sustainable epidemic trajectories (avoid epidemic extinction) at levels of concurrency found in recent surveys in sub-Saharan Africa. Efforts to support the concurrency hypothesis with a statistical correlation between HIV incidence and concurrency prevalence are not yet successful. Two decades of efforts to find evidence in support of the concurrency hypothesis have failed to build a convincing case.

Cross-species transmission of simian retroviruses: how and why they could lead to the emergence of new diseases in the human population

The HIV-1 group M epidemic illustrates the extraordinary impact and consequences resulting from a single zoonotic transmission. Exposure to blood or other secretions of infected animals, through hunting and butchering of bushmeat, or through bites and scratches inflicted by pet nonhuman primates (NHPs), represent the most plausible source for human infection with simian immunodeficiency virus (SIV), simian T-cell lymphotropic virus (STLV) and simian foamy virus. The chance for cross-species transmissions could increase when frequency of exposure and retrovirus prevalence is high. According to the most recent data, human exposure to SIV or STLV appears heterogeneous across the African countries surveyed. Exposure is not sufficient to trigger disease: viral and host molecular characteristics and compatibility are fundamental factors to establish infection. A successful species jump is achieved when the pathogen becomes transmissible between individuals within the new host population. To spread efficiently, HIV likely required changes in human behavior. Given the increasing exposure to NHP pathogens through hunting and butchering, it is likely that SIV and other simian viruses are still transmitted to the human population. The behavioral and socio-economic context of the twenty-first century provides favorable conditions for the emergence and spread of new epidemics. Therefore, it is important to evaluate which retroviruses the human population is exposed to and to better understand how these viruses enter, infect, adapt and spread to its new host.

Male circumcision for HIV prevention: current evidence and implementation in sub-Saharan Africa

Heterosexual exposure accounts for most HIV transmission in sub-Saharan Africa, and this mode, as a proportion of new infections, is escalating globally. The scientific evidence accumulated over more than 20 years shows that among the strategies advocated during this period for HIV prevention, male circumcision is one of, if not, the most efficacious epidemiologically, as well as cost-wise. Despite this, and recommendation of the procedure by global policy makers, national implementation has been slow. Additionally, some are not convinced of the protective effect of male circumcision and there are also reports, unsupported by evidence, that non-sex-related drivers play a major role in HIV transmission in sub-Saharan Africa. Here, we provide a critical evaluation of the state of the current evidence for male circumcision in reducing HIV infection in light of established transmission drivers, provide an update on programmes now in place in this region, and explain why policies based on established scientific evidence should be prioritized. We conclude that the evidence supports the need to accelerate the implementation of medical male circumcision programmes for HIV prevention in generalized heterosexual epidemics, as well as in countering the growing heterosexual transmission in countries where HIV prevalence is presently low.